In the field of the nuclear industry, different types of radioactive aqueous liquid effluents are produced during reprocessing, such as:                aqueous effluents comprising fission products resulting from operations for separating fission products of uranium and of plutonium in the reprocessing of used fuel;        aqueous effluents comprising dissolution fines and insolubles stemming from shearing and dissolution operations, for example of structural elements and metal sheaths;        aqueous effluents resulting from operations for rinsing the evaporators.        
These aqueous effluents, because of their high radiological activity, cannot be discharged into the environment and are therefore intended to be conditioned so that the radioactive elements and the radioactivity issued from the latter are trapped.
To do this, one of the standard solutions for conditioning this type of effluents, since the early 70s, is vitrification which consists of solidifying said effluents in a glassy matrix, the resulting product thereby forming an ultimate waste suitably conditioned for long-term storage.
In order to facilitate vitrification, the aqueous effluents containing radionuclides are led to being preconcentrated before vitrification as such, so as to remove the water present in these effluents and also denitrate them.
This preconcentration step may be carried out according to one of the following embodiments:                by distillation of the nitric acid conventionally contained in these aqueous effluents;        by making an azeotrope with the glycerin followed by distillation;        by burning the effluents in the presence of a liquid fuel; or        by calcining said effluents, the latter route being the one presently used in French vitrification operations.        
Calcination of liquid effluents comprising radionuclides is achieved conventionally in a calcination reactor, which may for example be an aerosol reactor, a reactor of the rotary drum calciner type or further a reactor with a fluidized bed.
Upon applying the calcination operation, two important problems may occur.
Firstly, certain nitrates, resulting from the action of nitric acid on the chemical elements present in the effluents, as this is the case for sodium nitrate, have a very low melting point which, at the end of the calcination operation, generates a viscous and tacky calcine which may generate clogging of the reactor in which the calcination is carried out. Adding glucose to the effluents, as mentioned in document U.S. Pat. No. 4,943,395, may contribute to promoting denitration and thereby limit partly the aforementioned clogging problem. In order to completely prevent this clogging problem, it may be also necessary to add to the effluents, inorganic adjuvants, such as aluminum nitrate or iron nitrate, which, in order to be effective have to be incorporated at high contents, which may range up to 50% by mass in the final composition of the calcine.
Secondly, the ruthenium potentially present in the radioactive aqueous liquid effluents may be led under the conditions for applying calcinations, to be oxidized into volatile species and to thereby escape into the environment. In order to overcome this problem, certain authors have proposed adding to the solution a reducing agent, in particular glucose, as proposed in the aforementioned document.
As regards calcination of the effluents before vitrification, the following drawbacks emerge from the embodiments of the prior art:                impossibility for the glucose used as reducing agent, of completely and concomitantly settling the problems related to oxidation of ruthenium and to the viscous and tacky aspect of the calcine at the end of the operation;        dilution of the radioactive elements to be conditioned, by adding inorganic adjuvants, which have the consequence of increasing the number of produced glass packets and therefore reducing the throughput of the vitrification lines and increasing the cost of storage.        
The authors of the present invention thus propose to develop a novel method for treating radioactive nitric aqueous effluents possibly comprising ruthenium, so that during the subsequent calcination, the problems related to the tackiness of the calcine and to the possible formation of volatile ruthenium oxide are solved, without it being necessary to resort to the use of inorganic adjuvants as mentioned above.